Effect of the Temperature on Wettability and Optimum Wetting Conditions for Maximum Oil Recovery in a Carbonate Reservoir System
M. Adeel Sohal
Erik G. Søgaard
The additional oil recovery from fractured and oil-wet carbonates by ionically modified water is principally based on changing wettability and often attributed to an improvement in water-wetness. The influence of different parameters, such as dilution of salinity, potential anions, temperature, pressure, lithology, pH, and oil acid and base numbers, to improve water-wetting has been tested in recovery experiments. In those studies, the temperature is mainly investigated to observe the reactivity of potential anions (sulfate and borate) at different concentrations. However, the influence of systematically increasing the temperature on wetting conditions has not been thoroughly investigated. In this experimental study, the effect of different temperatures on wettability for brines of different ionic strength and composition has been investigated in depth. A series of flotation experiments was conducted at 23, 50, and 100 °C using Dan outcrop chalk. The effect of each individual variable on the wetting condition was tested independently. The brines included seawater, seawater without sulfate, seawater (augmented with 2–4 times sulfate), and seawater containing borate instead of sulfate. All brines were diluted 2, 4, 10, 20, and 100 times. It was observed that, as the temperature increased, the water-wetness decreased for seawater and seawater dilutions; however, the presence of elevated sulfate can somewhat counter this trend because sulfate increased oil-wetting.